Field of Invention
The present invention relates to a method and system for die compensation and restoration using high-velocity oxy-fuel (HVOF) thermal spray coating and plasma ion nitriding, and more particularly, to a method and system for die compensation and restoration using HVOF thermal spray coating and plasma ion nitriding, whereby a particular part (damaged part) of a press die that causes formation of fine curves at a door of a vehicle, may be compensated for and restored to its original state.
Description of Related Art
Vehicle design has been regarded as important as performance to meet consumers' needs. Thus, there has been a need for the development of a hard-to-form production technique to implement complicated curved surface design for vehicles.
One such example is a cover panel of a vehicle is manufactured using a press die.
However, when the cover panel of the vehicle is manufactured using the press die, a defect, such as a fine curve (see FIG. 1), occurs in the cover panel of the vehicle due to a tension balance difference formed on the cover panel of the vehicle by a damaged part of the surface of the die.
Thus, as an example of the related art for compensating for a fine curve formed on the cover panel, a compensation (repair) method, whereby a damaged part of the die is restored to its original shape by performing hardfacing or overlay welding, such as arc welding, using a welding rod at the damaged part of the die, has been implemented.
However, when welding is performed on the damaged part of the die, it is difficult to control welding thickness, and thermal deformation of a substrate occurs, and a period for hardfacing or overlay welding is long, and a plurality of compensation numbers are required to perform precise dimensioning on the damaged part of the die.
In addition, the surface of the die that is restored by hardfacing or overlay welding, such as arc welding, is plated with chromium. However, it is not easy to control the thickness of the chromium plating layer, and due to a hardness difference in surface caused by the thickness of the plating layer, when the die is heated and vertical operations are repeatedly performed several thousands of times with a strong pressure during a press work, the plating layer is inevitably peeled off, and the die should be periodically re-plated.
It is difficult to use such a chromium plating method at 400□ or more, and due to a carcinogenic material having stronger toxicity than arsenic (As) or cadmium (Cd), such as Cr6+, environmental problems may occur during manufacture.
In order to solve the above-mentioned disadvantages of the compensation method of the die using hardfacing or overlay welding, a repair technique for alloying the damaged part of the die with high strength by repeatedly performing operations supplying metal powder to the damaged part of the die at a predetermined height, irradiating laser beams with low heat input onto the damaged part of the die at high velocity so as to form a molten part and simultaneously rapidly cooling the molten part by cooled air, is disclosed in Korean Patent Application Publication No. 10-2001-0067981 (published on Jun. 22, 2011).
However, the technique for repairing a local part of the die using laser beams with low heat input has overcome the disadvantages of hardfacing or overlay welding, such as arc welding; however, since an one-time stacking height of the metal powder is in the range of 0.8 to 1.2 mm, the technique is not suitable for a technique for compensating for a fine curve of the die that requires a compensation technique in units of micrometer, and due to an increase in manufacturing costs and hardfacing or overlay welding time caused by an additional rapid cooling process for high-strength alloying, efficiency is lowered.
As another die restoration method according to the relate art, a die restoration method including an ion-nitrided surface is disclosed in Korean Patent Application Publication No. 10-2007-0107966 (published on Nov. 8, 2007).
However, it is just adopted to include the ion-nitrided surface formed by ion nitriding that is an eco-friendly technique by replacing a die restoration method using chromium plating according to the related art. A detailed material for a hardfacing or overlay welding layer and types of dies and detailed conditions for an ion nitriding process and their procedures are not disclosed in the above reference and thus the effect of die restoration is insignificant.
As other related arts, a tungsten inert gas (TIG) welding or mixture powder coating method is used to repair a die manufactured using thermally spray-formed steel, or a technique for partially performing hardfacing or overlay welding by forming a low-temperature spray coating layer on a repair part of the die manufactured using thermally spray-formed steel and then by applying electric welding or low-temperature spray stacking process, is used.
However, there is no example in which a partial compensation technique using spray coating stacking is applied to a press die manufactured using spheroidal graphite cast iron (material containing a small amount of magnesium (Mg) in which graphite exists in a spheroidal form and which has improved strength and flexibility compared to general gray cast iron) as a substrate. Therefore, the development of the partial compensation method of the die manufactured using spheroidal graphite cast iron is urgently required.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.